1. Field of the Invention
The invention relates to a recording liquid to be attached in a droplet state to an object for the purpose of recording on the object, to a liquid cartridge having this recording liquid accommodated therein, and to a liquid discharge device and a liquid discharge method of forming an ink accommodated in this liquid cartridge in a droplet state and discharging it onto an object from a discharge nozzle.
2. Description of the Related Art
A printer device of an inkjet system feeds an ink of a recording liquid into an ink discharge head for discharging the ink onto recording paper which is an object from an ink cartridge having the ink accommodated therein, discharges the ink in a droplet state onto the recording paper through a nozzle from the ink discharge head and impacts the ink onto the recording paper, thereby printing images or letters. A printer device using this inkjet system has such an advantage that it is easy to attain low running costs, miniaturization of device and colorization of printed images.
Examples of an inkjet recording system include a diffraction system, a cavity system, a thermojet system, a Bubble Jet (registered trademark) system, a thermal inkjet system, a slit jet system, and a spark jet system.
An ink used for such an inkjet recording system is required to cause no nozzle clogging. With respect to the nozzle clogging, for example, a fine bubble generated in the ink is one of primary factors.
Though a prescribed amount of a gas such as air is dissolved in an ink, when the solubility of the gas decreases with an increase of the temperature, the gas which has not been completely dissolved in the ink is separated and becomes a fine bubble in the ink. Concretely, in a printer device, when the temperature of an ink present in an ink cartridge from which the ink is fed into an ink discharge head or in an ink discharge head increases, the gas presented in a dissolved state in the liquid is released, whereby a fine bubble is formed in the ink.
In the ink discharge head, when such a fine bubble is present, there may be a possibility that the bubble comes into the nozzle, whereby deficient discharge is caused such that the ink cannot be discharged or the discharge direction of the ink is deviated due to the bubble which has come into the nozzle, blurring or deletion is caused on a printed image, and the quality of an image or letter is deteriorated.
In particular, an inkjet recording system by a thermal system or a Bubble Jet system is a recording system in which heat energy is applied to an ink, thereby forming the ink into a fine droplet, which is then discharged from a nozzle. Concretely, an ink is quickly heated by a heater as a heat energy source, formed in a droplet state by a pressure due to an air bubble formed by film boiling of the ink and discharged from a nozzle. For that reason, in the thermal system and the Bubble Jet system, the heat is accumulated in the vicinity of the heater, the temperature of the ink present in an ink passage is very likely increased, and the gas which has not been completely dissolved in the ink is separated, whereby a fine bubble is likely formed. Thus, in the thermal system and the Bubble Jet system, there may be a possibility that deficient discharge such as non-discharge of ink and bending of the discharge direction is remarkably caused.
In order to improve these problems, for example, JP-A-2001-2964 (Patent Document 1) and JP-A-10-46075 (Patent Document 2) propose to blend a propylene oxide addition polymer of a lower alcohol in an aqueous pigment ink. However, in these proposals, it is difficult to thoroughly control the formation of a fine bubble in an ink, and therefore, more improvements are demanded.
For example, JP-A-7-70491 (Patent Document 3), proposes to contain an ethylene oxide adduct of a higher secondary alcohol alkoxylate in an ink. This Patent Document 3 describes that this ink is excellent in discharge stability at the time of high-frequency drive, permeability into recording paper and dryness. However, in this ink, even when a compound having only ethylene oxide added to a higher secondary alcohol alkoxylate is contained, it is difficult to improve nozzle clogging due to a fine bubble. Concretely, when a compound having only 7 moles or more of ethylene oxide added therein is contained in an ink, bubbling is vigorous, and nozzle clogging becomes remarkable, too.
Accordingly, the ink used in the inkjet recording system is not only required such that bubbling is suppressed and that nozzle clogging is not caused but also required such that when printing is carried out on plain paper, i.e., so-called wood-free paper, such as copying paper and a writing pad, a lowering of optical density and deterioration of quality of images or letters such as bleeding of boundaries and unevenness of mixed color are not generated.
With respect to these requirements, for example, JP-A-2000-154342 (Patent Document 4) proposes to use a coloring matter resulting from treating a water-insoluble coloring matter with a polymer containing a sulfonic acid (salt) group and/or a polymer containing a phosphoric acid (salt) group and to further add a polymer containing a carboxylic acid (salt) group in an ink.
JP-A-8-290656 (Patent Document 5) proposes to blend an alginic acid having a ratio of D-mannuronic acid to L-glucuronic acid in the range of from 0.5 to 1.2 in an ink.
In addition, JP-A-8-193177 (Patent Document 6) proposes to blend at least one surfactant selected from fluorine based or silicon based surfactants and an alginic acid salt in an ink.
However, even in the inks described in the Patent Documents 4 to 6, it is difficult to obtain satisfactory results for preventing nozzle clogging and deterioration of quality of images or letters, and therefore, more improvements are demanded.
A problem due to a fine bubble formed in an ink is more remarkably caused in a printer device capable of achieving high-speed printing on recording paper, namely a line type printer device in which a range substantially the same as the width of recording paper is the discharge range of the ink (see, for example, JP-A-2002-36522 (Patent Document 7)).
That is, in the line type printer device, nozzles are arranged in parallel over a length substantially the same as the width of recording paper, and plural pressure producing elements for pressing an ink opposing to the respective nozzles are also provided over a length substantially the same as the width of recording paper.
On the other hand, in a serial printer device, since printing for one line is carried out by moving an ink discharge head in a width direction of recording paper, the number of pressure producing elements is smaller than that of those provided in the line type printer device.
For that reason, in comparison with the serial printer device, since in the line type printer device, many pressure-generating elements are heated at once in carrying out printing, the temperature of the ink is liable to increase. Thus, in the line type printer device, a fine bubble is likely formed so that a fault due to the formed fine bubble is remarkably caused.
In the line type printer device, since an ink is fed into all of the nozzles provided in a range substantially the same as the width of recording paper, an ink passage for feeding an ink into each nozzle from an ink cartridge is formed in a length substantially the same as the width of recording paper, too. For that reason, in the line type printer device, a distance of from the ink cartridge to each nozzle is long, the structure is complicated, a formed bubble is hardly removed, and a fault due to the fine bubble is remarkably caused.
In the line type printer device, since a discharge space of the ink in every nozzle line at which plural nozzles are arranged in parallel is extremely short, it is necessary to use an ink having excellent permeability into recording paper. In the line type printer device, when an ink having excellent permeability into recording paper is applied to plain paper or the like, there maybe a possibility that the optical density is lowered because the ink excessively bleeds in a depth direction, namely a thickness direction of the plain paper.
In the line type printer device, for example, when so-called color printing in which inks having a different color from each other are discharged onto recording paper to achieve printing is carried out, since before the ink impacted on the recording paper sufficiently permeates into the paper, droplets of a next color are impacted one after the other, there may be a possibility that bleeding of boundaries between the respective colors or unevenness of mixed color is caused.